(a) Field of the Invention
This invention relates to a press-feed units which operate to feed a length of stock material, most commonly strip material, to a press in synchronism with press operation. It is particularly concerned with such units of the type having a body adapted for fixing adjacent the press and a transport section reciprocable relative to the body by a pneumatic piston and cylinder assembly, during guided reciprocation the stock being clamped to the transport section during the forward feed strokes of the latter.
(b) Description of the Prior Art
With present units of the foregoing type, if multiple duplex or double-acting arrangements are required they employ entirely different units and/or complicated synchronising control means. The main object of the invention is to overcome these disadvantages, enabling a whole family of feed units to be assembled from basic main sub-assemblies common to several units. A further object is to provide a unit which is usable in a multiple arrangement capable of operating at unusually high speed while being no more, or in some cases less, complicated than existing multiple arrangements.
It is common practice to couple two units together, to provide a right-hand master unit and a left-hand slave unit which operate in tandem while respectively gripping the opposite side edges of wide strip or sheet material. In the past the control valve section of the master unit has been operated in dependence on press movement, as for a single unit, and the controlled pressure transport cylinder feed has been split between the master and slave units. Accurate splitting of this pressure feed is necessary for satisfactory duplex operation of the units, so that setting up is a difficult and complex procedure.
Instead of two side-by-side units operating in tandem, to cooperate in feeding strip stock simultaneously, they may operate out of phase to feed the stock alternately. Such a double-acting arrangement can theoretically feed the stock at a speed twice that of a single unit, but in the past very complex press/feed control arrangements have been necessary to synchronise the units.